The "Responsible" field in a work request identifies the single entity that is responsible for resolving the request. It is either a UW userid, or an e-mail address of another work tracking system, typically "request@ist".
This is potentially distinct from the owners of a request, who are responsible for doing the actual work. It is usually the person who the requesters of the work have personal contact with.
The default for the "Responsible" field is the first name in the list of owners that has permission to modify requests, if any of them do. Otherwise it's just the first name in the list.
When specifying this field in a customized sort or display, any of the names "responsible" or "Responsible" can be used.